Method swap

chapter19/src/main/java/com/seaofnodes/simple/Ary.java:121–129

( int i, int j )

    }

    public E swap( int i, int j ) {
        range_check(i);
        range_check(j);
        E tmp = _es[i];
        if( i==j ) return tmp;
        _es[i] = _es[j];
        _es[j] = tmp;
        return tmp;
    }


    /** @param c Collection to be added */